A new personalized cancer vaccine used alongside the immunotherapy drug Keytruda cut the risk of melanoma returning or patients dying by 42% in a major clinical trial, researchers reported.

The trial enrolled 1,137 adults with melanoma who had already had their tumors removed surgically. About two-thirds received Keytruda plus the experimental vaccine called Intismeran. The rest received Keytruda with a placebo. Over two years, the vaccine also reduced the risk of melanoma spreading by 38% compared to immunotherapy alone.

Intismeran uses mRNA technology, the same approach as some Covid vaccines. Each vaccine is personalized using genetic information from a patient's own tumor to train their immune system to recognize and attack cancer cells.

Prof Pippa Corrie, a consultant medical oncologist at Addenbrooke's Hospital in Cambridge who helped run part of the study, said personalization represents "the next step up" in cancer treatment. She noted the trial provided "the first proof of principle" for this approach.

Tony Chapman, a 75-year-old from Corby, enrolled after his melanoma returned in his lymph nodes following initial surgery. He remains cancer-free three years later, though he does not know whether he received the vaccine or placebo.

Independent experts praised the results. Professor Alan Melcher from the Institute of Cancer Research in London, who was not involved in the research, called them "very impressive" but cautioned that "we can't assume from one melanoma trial that the same approach will work across all cancers, and longer follow-up will be important to understand the effect on overall survival."

Drug manufacturers MSD and Moderna are testing the same approach against kidney, bladder, and lung cancers. Both companies said they are engaging with medicine regulators and may file for approval next year. The trial will continue to monitor whether the vaccine affects long-term survival.

The full results will be presented at the European Society of Medical Oncology conference in Madrid but have not yet been published in a peer-reviewed journal.